In order to meet varying users' requirements, illuminated keyboards that integrate lighting modules to generate illumination have been developed and introduced on the market to attract consumers and provide an extra feature to increase their purchase motivation. While emphasizing the illuminated function, many producers also endeavor to reduce total thickness of the keyboard module so that it can be widely adapted to notebook computers or desktop computers highlighting thin and light design.
Conventional thin illuminated keyboards, for instance, R.O.C. patent No. M352718 discloses an illuminated keyboard which comprises a key set unit, a thin film circuit board and a lighting unit. The thin film circuit board includes a thin film bottom layer, a thin film middle layer on the thin film bottom layer and a thin film top layer on the thin film middle layer. The thin film bottom layer has a top surface with a plurality of protrusive reflective light guide points formed thereon. Light emitted from the lighting unit is reflected and scattered upwards through the light guide points. R.O.C. patent No. M368835 discloses a light guide plate for illuminated keyboards. The light guide plate includes a transparent base plate and a circuit unit laid on the top surface of the transparent base plate with conduction contacts formed thereon. The transparent base plate has a plurality of light guide points formed on the bottom surface thereof to divide the bottom surface into a plurality of light guide zones. When light projects to a lateral side of the light guide plate, it is refracted upwards through the light guide points to generate illumination.
Moreover, R.O.C. publication No. 200945112 also discloses a similar structure about a keyboard equipped with a self-illuminated circuit board. It includes a key module and a circuit board. The circuit board has at least one base plate made of a flexible light guide material and laid with circuits and a light emitting portion. The circuit board receives light from the light emitting portion and projects the light upwards to the key module.
All the aforesaid conventional techniques include a base plate made of a light guide material and laid with circuits, and the circuit board and light guide plate are integrated into a single element to shrink the thickness and size of the keyboard. However, in their keyboard modules, light is guided to project to the upper side of the keyboard through the light guide points on the circuit board or other light guide structures. Such a light guide structure makes the light scatter outside from the circuit board, and is difficult to condense the light to the area where the light is needed. Moreover, users are difficult to identify the character symbol on each keycap in such a condition. The light cannot be used effectively, hence more light emitting elements has to be installed. As a result, total power consumption increases and a greater amount of heat is generated.